High compression race motor options?

[sureshot007]

I'm in the planning stage for next season, and the idea of getting more power from the motor came up. After some searching on the internet, it looks like this is the place to ask some questions (since you guys have the experience).

Goal: More horsepower
Restrictions: Budget, reliability, pump gas, (I'm sure there are others, but I can't think of them right now)
Truck: 1994 Jeep Cherokee 4.0

Currently, I have a bone stock 4.0. I would like to relocate the crank sensor with the Hesco kit so that I can run a lightweight flywheel (if I can ever figure out one that will fit). So I'd like to get it to rev a little faster, and squeeze a little more power out of it. I was thinking about increasing the compression ratio to something between 10-11:1 (something I can safely run off 93). I'll obviously need a new cam to make it come to life.

I can't afford to build this thing up with all the best parts, but say I have a budget of $2k total. Events are less than 150 miles, and we plan to run 3-4 events a year, so as long as the motor can survive a season before a rebuild, I'm ok with that. Luckily, the displacement limit is 6.2 liters, so I don't have to worry about going over that.

So, with that in mind, what sort of suggestions do you guys have?

[gradon]

4-weight crank from a 87-90 wrangler(YJ), +.060" KB 945 pistons($400), 505 rollercam that's good for mid-high range power($1200), port&polish the head and combustion chamber, full 2.5" exhaust. Fidanza makes a standard flywheel for out Jeeps. I asked them about making a light-weight version and they needed a minimum order of 10 to continue.

[herbiehind]

bore only what you need so you can do it again later .

[sureshot007]

What's special about the wrangler crank?

[Cheromaniac]

What's special about the wrangler crank?

The '87-'90 4.2 crank has only 4 counterweights (lighter) and the nose is the same length as that of the 4.0 crank, so you can bolt the harmonic balancer on without either using a spacer or cutting 1cm off the nose.

[SIXPAK]

I would NOT opt for the 4cw crank. Been down that road and won't do it again. Heck, I'll even sell you the premo 4cw one out in the garage I tried to run!

[The Beast]

What happened to you and your 4WC. Mines perfectly fine, I can put my hand on the block and barely feel it run. Maybe you got a bad one??? Sorry I'm new to this forum.

[SIXPAK]

If you are not going to rev this thing past 5200 or so you will be fine I think. But read this thread.
http://www.jeepstrokers.com/forum/viewt ... f=5&t=1153

[sureshot007]

I think revving past 5200 will be required. I was hoping for an operational rpm range up to 6500.

[Missourian]

I think revving past 5200 will be required. I was hoping for an operational rpm range up to 6500.

Wow, I did not know these engines were capable of anything beyond 5k RPM!

[SIXPAK]

I would opt for the 12 cw version then. And I'm not saying put it in and forget it. A steady dose of manafluxing should be done in the off season to check for cracks!

[I6FAN]

The 3rd order harmonic is ~5400 rpm, 2.5 order is 6480 rpm, and 2nd order is 8100 rpm [assuming 5400 is the 3rd order]. 2.5 and 2 order are not as severe as 3rd order. One of the things you can do to control the amplitudes of the harmonics is reduce rotateing and recip weight. Stock rods work great, but a good I beam forged rod is ~60grams lighter than the stock 4.0 rod [about 100 grams than 4.2], and a good light weight piston [forged] is about 80 grams lighter than stock; which is about 17% reduction. You could go to a light weight pin as well and save a few grams there as well. In this application, don't really need the forged items for their superior strength, but rather for their lighter weight. This should reduce the amplitude of torsion. A well prepped crank would be good too; polished and shot peened. This is kind of a bummer to me because I wanted to biuld a 5500 rpm motor, and be able to hold it there.

Lee over at HESCO says to effectively dampen the harmonic, with proper mass, it needs a 14" diameter balancer which is not phsically feasible. He tried to make one of proper mass by increasing its thickness and retaining stock diameter, so it was more cylindrical shaped, and it snapped off in the dyno room! Usually the end of the crank that breaks is the end opposite of the flywheel. I understand that you can rev through the harmonic, but you can't "hold" it there. I asked if you are limited by how many times you can do this [cycles], but didn't get a clear answer on this, but I would think it is cycle limited to some degree.

[sureshot007]

Anyone know anything about the 505 Performance 5L stroker kit?

http://www.shop.505performance.com/prod ... egoryId=25

[gradon]

My brother has the 5.0L roller kit(actually 4.9l w/ the +.060" pistons) with their "most radical cam" and 34.Xcc dish pistons for a SCR of 8.75:1(it's gonna see boost someday). We need to take the pistons back out and check the ring gaps cause the crank stopped spinning once we put the last two pistons in(he's taking his sweet ole time w/ the build).

[sureshot007]

I'd definitely like to hear what your thoughts are once it gets running.